Liverpool defender Mamadou Sakho has failed a drugs test and will not play in today's game against Newcastle, it is understood

The alleged offence relates to the Reds' Europa League second-leg tie at Manchester United and is believed to concern a so-called 'fat-burning' substance.

Press Association Sport understands the France international is highly likely to request his B sample be tested, with the deadline for that request set for Tuesday.

Sakho has not been suspended either by the club or UEFA, but it is understood that after discussion between the club's owners Fenway Sports Group, manager Jurgen Klopp and the player himself it was decided the centre-back should not play in the immediate future, even though he is still eligible for Premier League matches and Thursday's Europa League semi-final first leg in Villarreal.

"Yesterday, Friday 22nd April 2016, a formal communication was received from UEFA stating that they are investigating a possible anti-doping rule violation by Mamadou Sakho," it said.

"The player will respond to UEFA on the matter. The player is currently not subject to any playing suspension.

"However, the club, in consultation with the player, has decided that while this process is followed the player will not be available for selection for matches.

"There will be no further comment at this time."

The club have been pro-active in their response to the alleged doping violation - consulting fully with UEFA and the Football Association - and while Sakho is technically still available to play it was felt the best course of action was to withdraw the player from selection and it is understood Sakho himself was fully behind the decision.

There will be no disciplinary action for the club to face - that can only kick in if two players in same season are found to have had doping violations - and there is absolutely no risk to their continued participation in the Europa League.

Sakho's fellow central defender Kolo Toure was suspended for six months after failing a drugs test while at former club Manchester City in February 2011 having tested positive for bendroflumethiazide, a weight-loss drug contained within "water tablets" recommended to him by his wife.